Originally Posted by bayview
Agreed as long as the engine gets to proper operating temp dont worry about boost or other myths.
Best fuel consumption vs speed will be at a speed that keeps the bow down. any excessive wave making is wasting fuel. Forget all the math and find the speed where your boat doesn't make waves. Notice that this has nothing to do with rpm, engine make or specifications just your hull moving as fast as possible while making the least water disturbance.
Many (most?) turbocharged engines have a lower compression ratio than NA. I believe the "on boost" recommendation probably stems from this with the thought that if the turbo is providing pressure, then the combustion process is probably more complete and internal temperatures are more likely to be where they should be. The turbo engines in our boat do not reach normal operating temperature when idling along at 35 HP per side @ 9 KTS.